Magnetostratigraphy of Late Eocene - Early Oligocene strata from the CRP-3 core, Victoria Land Basin, Antarctica
Magnetostratigraphy of Late Eocene - Early Oligocene strata from the CRP-3 core, Victoria Land Basin, Antarctica
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南极洲维多利亚陆地盆地 CRP-3 核心的晚始新世 - 早渐新世地层的磁性地层
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发表时间：
2001
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通讯作者：
K. Verosub
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作者：
F. Florindo;G. Wilson;A. Roberts;L. Sagnotti;K. Verosub
罗伯茨角项目于1999年春季成功完成，钻出了位于CRP-2/2A钻孔以西2公里的939.42米的CRP-3钻孔。CRP-3岩心包括790 m的新生代（冰期-）海相层序，与下伏的泥盆系基底岩被一层年龄不确定的约30 m厚的白云岩砾岩分离。本文介绍了古地磁研究的结果，包括与磁极时间尺度（MPTS）的相关性和在CRP-3区恢复的新生代层序的年龄模型。新生代沉积层序的古地磁行为总体稳定，磁铁矿是主要的磁载体。将CRP-3岩心新生代层序的磁极性地层学划分为4个磁带：R1为极性反转上部（0 ~ 340.8 mbsf）， N1为极性正侧（340.8 ~ 627.3 mbsf）， R2为极性反转上部（627.3 ~ 760.2 mbsf）， N2为极性正侧（760.2 ~ 788.8 mbsf）。磁带R1、N1和R2也包含极性相反的薄层，这些薄层可以解释为短极性层（对应于海洋磁异常记录中识别的“微小摆动”）或地磁偏移。在340 mbsf以上，硅藻和钙质纳米化石生物地层和87Sr/86Sr年龄表明R1磁带与MPTS的Chron C12r相关。在340 mbsf以下，我们将磁带N1和R2分别与MPTS的C13n和C13r时间进行了初步的关联。然而，在R1以下，磁极记录不受生物地层或87Sr/86Sr年龄的限制。对比结果表明，该岩心始新统-渐新统界线（33.7 Ma）位于岩石地层13.1亚单元内，厚度约为718 mbsf。由于缺乏独立的年代地层学约束，很难解释新生代层序基底的年龄，但磁地层学表明其最小年龄为C13r （c. 34 Ma）。
The Cape Roberts Project was successfully completed in the austral spring of 1999 with drilling of the 939.42-m CRP-3 drillhole, located 2-km west of the CRP-2/2A drillhole. The CRP-3 core comprises a 790-m Cenozoic (glacio-) marine sequence separated from underlying Devonian basement rocks by a c. 30-mthick dolerite conglomerate of undetermined age. Here, we present the results of a palaeomagnetic study, including correlation to the magnetic polarity time scale (MPTS) and an age model for the Cenozoic sequence recovered in CRP-3. The palaeomagnetic behaviour of the Cenozoic sedimentary sequence is generally stable, and magnetite is the main magnetic carrier. The magnetic polarity stratigraphy of the Cenozoic sequence in the CRP-3 core is subdivided into four magnetozones: R1 is an upper interval of dominantly reversed polarity (0-340.8 mbsf), N1 has dominantly normal polarity (340.8-627.3 mbsf), R2 has dominantly reversed polarity (627.3-760.2 mbsf), and N2 has normal polarity (760.2-788.8 mbsf). Magnetozones R1, N1, and R2 also contain thin intervals with opposite polarity, which are interpreted as representing either short polarity intervals (corresponding to “tiny wiggles” identified on marine magnetic anomaly records) or geomagnetic excursions. Above 340 mbsf, diatom and calcareous nannofossil biostratigraphy and 87Sr/86Sr ages suggest that magnetozone R1 correlates with Chron C12r of the MPTS. Below 340 mbsf, we tentatively correlate magnetozones N1 and R2 with chrons C13n and C13r of the MPTS, respectively. However, below R1, the magnetic polarity record is not constrained by biostratigraphy or 87Sr/86Sr ages. Our correlation implies that the Eocene-Oligocene boundary (33.7 Ma) in the CRP-3 core should lie within lithostratigraphic sub-Unit 13.1, at about 718 mbsf. Lack of independent chronostratigraphic constraints makes it difficult to interpret the age of the basal part of the CRP-3 Cenozoic sequence, but the magnetostratigraphy suggests a minimum age of Chron C13r (c. 34 Ma).